Effect of secondhand smoke on occupancy of nicotinic acetylcholine receptors in brain

Bone Resorption in Apical Periodontitis Enhanced by Cigarette Smoke Inhalation: Histometric, Immunohistochemical, and Microtomographic Analysis in Rats

INTRODUCTION

This study evaluated the effects of cigarette smoke inhalation (CSI) on apical periodontitis (AP) induced in rats by histometric, immunohistochemical, and microtomographic analysis.

METHODS

A total of 32 male Wistar rats were divided into 4 experimental groups (n = 8): control, CSI, AP, and CSI + AP. Rats in the CSI and CSI + AP groups inhaled cigarette smoke by remaining inside a smoking chamber for 8 minutes 3 times a day for 50 days. After 20 days of smoke inhalation, rats in the AP and CSI + AP groups had the pulp of their first right lower molar exposed to induce AP. Blood was collected on day 50 to evaluate nicotine and serum cotinine levels. The animals' mandibles were removed for histologic processing to evaluate bone resorption by histometric, immunohistochemical (receptor activator of nuclear factor kappa B ligand/osteoprotegerin), and microtomographic analysis. The Student t test was applied.

RESULTS

Histometric analysis showed a larger area of bone resorption (P < .05) and microtomographic analysis found greater resorption volume (P < .001) for the CSI + AP group compared with the AP group. The CSI + AP group presented a high RANKL immunostaining pattern compared with the AP group (P < .001).

CONCLUSIONS

CSI increased bone resorption caused by AP.

Addressing Intergenerational Inequity in Tobacco-Harm: What Helps Children of Smokers to Remain Nonsmokers?

INTRODUCTION

Children of people who smoke are more likely to take up smoking themselves. In Aotearoa New Zealand (NZ), adolescent smoking declined dramatically between 2000 and 2016 despite limited change in parental smoking, demonstrating that the cycle can be broken.

AIMS AND METHODS

This study aimed to identify modifiable factors associated with never smoking in Year 10 students (14-15 years) who had at least one caregiver who smoked. We used data from the Youth Insights Survey (2016 and 2018, pooled, N = 5,422) and identified students with at least one caregiver (mother, father, grandparent, other caregiver) who smoked (N = 2,205). To investigate modifiable factors potentially associated with nonsmoking we used logistic regression with marginally adjusted prevalence estimates.

RESULTS

Overall, 41% of students had at least one caregiver who smoked. In this group, the majority (65%) had never smoked themselves. After adjustment, never-smoking was more prevalent among students attending low-deprivation (more affluent) schools (73% had never smoked) compared to high-deprivation schools (44%); students not exposed to others' smoking inside the home (72%) or in cars (70%) in the past week compared to those exposed (59% and 51%, respectively); and students whose parents would be upset if they were caught smoking (68% vs 49% for those whose parents would not be upset), or who had high self-esteem (69% vs 55% for those with low self-esteem).

CONCLUSIONS

Modifiable factors independently associated with non-smoking in adolescents with caregiver(s) who smoked were: nonexposure to smoking inside the home and in cars, parental expectations of nonsmoking, and high self-esteem.

IMPLICATIONS

Even in countries like NZ with relatively low adult smoking rates, children's exposure to caregiver smoking may be prevalent, particularly in structurally disadvantaged populations. This study suggests that action to promote smokefree homes and cars, build high self-esteem in young people, and communicate expectations of non-smoking are likely to help children of people who smoke to remain nonsmokers. A comprehensive approach that also addresses "upstream" factors (eg, socioeconomic deprivation) and underlying causes of structural inequity (eg, institutional racism) is needed. Such policy and community action may help to break intergenerational cycles of tobacco use and health inequity.

Distribution of cholinergic nerve terminals in the aged human brain measured with [18F]FEOBV PET and its correlation with histological data

INTRODUCTION

[¹⁸F]fluoroetoxybenzovesamicol ([¹⁸F]FEOBV) is a positron emission topography (PET) tracer for the vesicular acetylcholine transporter (VAChT), a protein located predominantly in synaptic vesicles in cholinergic nerve terminals. We aimed to use [¹⁸F]FEOBV PET to study the cholinergic topography of the healthy human brain.

MATERIALS AND METHODS

[¹⁸F]FEOBV PET brain data volumes of healthy elderly humans were normalized to standard space and intensity-normalized to the white matter. Stereotactic atlases of regions of interest were superimposed to describe and quantify tracer distribution. The spatial distribution of [¹⁸F]FEOBV PET uptake was compared with histological and gene expression data.

RESULTS

Twenty participants of both sexes and a mean age of 73.9 ± 6.0 years, age-range [64; 86], were recruited. Highest tracer binding was present in the striatum, some thalamic nuclei, and the basal forebrain. Intermediate binding was found in most nuclei of the brainstem, thalamus, and hypothalamus; the vermis and flocculonodular lobe; and the hippocampus, amygdala, insula, cingulate, olfactory cortex, and Heschl's gyrus. Lowest binding was present in most areas of the cerebral cortex, and in the cerebellar nuclei and hemispheres. The spatial distribution of tracer correlated with immunohistochemical post-mortem data, as well as with regional expression levels of SLC18A3, the VAChT coding gene.

DISCUSSION

Our in vivo findings confirm the regional cholinergic distribution in specific brain structures as described post-mortem. A positive spatial correlation between tracer distribution and regional gene expression levels further corroborates [¹⁸F]FEOBV PET as a validated tool for in vivo cholinergic imaging. The study represents an advancement in the continued efforts to delineate the spatial topography of the human cholinergic system in vivo.

Cholinergic receptor binding in unimpaired older adults, mild cognitive impairment, and Alzheimer's disease dementia

BACKGROUND

Cholinergic neurotransmitter system dysfunction contributes to cognitive impairment in Alzheimer's disease and other syndromes. However, the specific cholinergic mechanisms and brain structures involved, time course of alterations, and relationships with specific cognitive deficits are not well understood.

METHODS

This study included 102 older adults: 42 cognitively unimpaired (CU), 28 with mild cognitive impairment (MCI), and 32 with Alzheimer's disease (AD) dementia. Each participant underwent a neuropsychological assessment. Regional brain α4β2 nicotinic cholinergic receptor binding (V_T/fp) was measured using 2-[¹⁸F]fluoro-3-(2(S)azetidinylmethoxy)pyridine (2FA) and PET imaging. Voxel-wise analyses of group differences were performed. Relationships between receptor binding and cognition, age, and cholinesterase inhibitor medication use were assessed using binding values in six prespecified regions of interest.

RESULTS

SPM analysis showed the group V_T/f_p binding differences in the bilateral entorhinal cortex, hippocampus, insula, anterior cingulate, thalamus, and basal ganglia (p < .05, FWE-corrected). Pairwise comparisons revealed lower binding in the AD group compared to the CU group in similar regions. Binding in the entorhinal cortex was lower in the MCI group than in the CU group; binding in the hippocampus was lower in the AD group than in the MCI group. AD participants taking cholinesterase inhibitor medication had lower 2FA binding in the bilateral hippocampus and thalamus compared to those not taking medication. In the CU group, age was negatively associated with 2FA binding in each region of interest (r_s = - .33 to - .59, p < .05 for each, uncorrected). Attention, immediate recall, and delayed recall scores were inversely associated with 2FA binding in most regions across the full sample. In the combined group of CU and MCI participants, attention was inversely associated with 2FA binding in most regions, beyond the effect of hippocampal volume.

CONCLUSIONS

Nicotinic cholinergic receptor binding in specific limbic and subcortical regions is lower in MCI and further reduced in AD dementia, compared to CU older adults, and is related to cognitive deficits. Cognitive decline with age may be a consequence of reduced cholinergic receptor density or binding affinity that may also promote vulnerability to other Alzheimer's processes. Contemporary modification of the "cholinergic deficit" of aging and AD may reveal opportunities to prevent or improve clinical symptoms.

Investigating the association between smoking, environmental tobacco smoke exposure and reward-related brain activity in adolescent experimental smokers

Reduced anticipatory reward‐related activity, especially in the ventral striatum (VS), may underly adolescent vulnerability to develop nicotine dependence. It remains unclear whether nicotine uptake caused by environmental tobacco smoke (ETS) exposure, known to be associated with future smoking, might prompt similar changes in the brain's reward system, rendering adolescents vulnerable for development of nicotine dependence. To address this question, we tested whether current ETS exposure and monthly smoking are associated with VS hypoactivity for non‐drug rewards in experimental smoking adolescents. One‐hundred adolescents performed a monetary incentive delay task while brain activity was measured using fMRI. To test the hypothesized relationship, we used a variety of approaches: (1) a whole‐brain voxel‐wise approach, (2) an region‐of‐interest approach in the VS using frequentist and Bayesian statistics and (3) a small volume voxel‐wise approach across the complete striatum. The results converged in revealing no significant relationships between monthly smoking, ETS exposure and reward‐related brain activation across the brain or in the (ventral) striatum specifically. However, Bayesian statistics showed only anecdotal evidence for the null hypothesis in the VS, providing limited insight into the (non‐)existence of the hypothesized relationship. Based on these results, we speculate that blunted VS reward‐related activity might only occur after relatively high levels of exposure or might be associated with more long term effects of smoking. Future studies would benefit from even larger sample sizes to reliably distinguish between the null and alternative models, as well as more objective measures of (environmental) smoking via using devices such as silicone wristbands.

Cumulative disadvantage as a framework for understanding rural tobacco use disparities

Traditional tobacco product (cigarettes and smokeless tobacco) and polytobacco use rates are significantly higher among rural adolescents and adults compared to their nonrural counterparts. Such disparities are due to several factors that promote tobacco use initiation and continuation, including individual-level psychopharmacological factors and structural-level factors such as fewer tobacco control efforts (e.g., fewer smoke-free policies and lower tobacco excise taxes), targeted tobacco marketing, less access to health-relevant resources, and more positive cultural norms surrounding tobacco use in rural communities. In this review, we use cumulative disadvantage theory as a framework for understanding how psychopharmacological and structural-level factors serve as drivers of tobacco use in rural areas. We start by describing how structural-level differences between rural-nonrural communities impact psychopharmacological influences and, when available, how these factors influence tobacco use. We conclude by discussing the interplay between factors, providing suggestions for ways to assess our application of cumulative disadvantage theory empirically and making recommendations for research and policy implementation in rural areas. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

A review of constituents identified in e-cigarette liquids and aerosols

INTRODUCTION

Identification of chemicals present in e-liquids and aerosols is a vital first step in assessing the human health effects of e-cigarettes. We aim to identify the qualitative and quantitative constituents present in e-cigarette liquids and aerosols.

METHODS

A comprehensive search of scientific databases included literature up to July 2020. A total of 28 articles met inclusion criteria; 18 articles assessed e-liquid constituents and 15 articles assessed aerosol constituents. Of these, 5 assessed constituents present in both mediums. We included English-language publications that examine qualitative and/or quantitative constituents in e-cigarette liquids and aerosols.

RESULTS

In total, articles identified 60 compounds in e-liquids and 47 compounds in aerosols. A total of 22 compounds were identified in both e-liquids and aerosols. These are: acenaphthylene, acetaldehyde, acetol, antimony, benzaldehyde, benzene, chromium, copper, diacetyl, formaldehyde, glycerol, lead, limonene, naphthalene, nickel, nicotine, nicotine-N'-oxides, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N-Nitrosonornicotine (NNN), propylene glycol, toluene, and vegetable glycerin. Some of the identified chemicals have been labeled as harmful, toxic, or cancerous through human, animal, and cell line studies. A variety of laboratory methods were used for analyses, which made reported levels less consistent.

CONCLUSIONS

E-liquids and aerosols contain a variety of chemicals with potential health effects from inhaling them. Further, secondhand health effects are unknown because of limited understanding of the dose of exposure by non-users. Identification of constituents in e-cigarettes is the first step to determine their risks to humans and support evidence-based regulations and health policies.

Trajectory of smoking behaviour during the first 6 months after diagnosis of lung cancer: A study from Taiwan

AIMS

To identify different classes of change pattern/ trajectory of tobacco smoking behaviour after diagnosis of lung cancer using multi-wave data and to explore factors associated with the class membership.

DESIGN

This is a multi-wave observational study.

METHODS

Smoking behaviour data were collected at diagnosis and then every month for 6 months from 133 newly diagnosed people with lung cancer who had recently quit smoking or continued to smoke at diagnosis. These patients were recruited from three medical centres and data were collected from May 2014 to January 2017. Smoking behaviour was assessed based on patients' self-reports on whether they smoked during the last month (yes/no) for a total of seven times. Mixture latent Markov model and logistic regression were used to analyse data.

RESULTS

Two latent classes of smoking trajectory were identified among recent quitters or current smokers of people with lung cancer, namely "perseverance for abstinence" and "indecisive for abstinence." Patients who were younger age (OR = 0.95, p = 0.026), exposure to second-hand smoke (OR = 3.35, p = 0.012) and lower self-efficacy for not smoking (OR = 0.96, p = 0.011) were more likely to belong to the class of "indecisive for abstinence."

CONCLUSIONS

Heterogeneous classes of smoking trajectory existed in newly diagnosed people with lung cancer. The risk factors associated with a less favourable smoking trajectory can be incorporated into tailored smoking-cessation programs for patients newly diagnosed with lung cancer.

IMPACT

The dynamic trajectory of smoking behaviour had not been adequately explored among newly diagnosed people with lung cancer. Two classes of smoking trajectory and the predictors associated with the class membership were identified. These findings suggest that the diagnosis of cancer is a teachable moment for smoking cessation. Patients with younger age, lower self-efficacy of not smoking and exposure to second-hand smoke at home need special attention.

Environmental Tobacco Smoke Exposure and Brain Functioning Associated with Smoking Cue-Reactivity and Inhibitory Control in Nonsmoking Adolescents

INTRODUCTION

Despite its well-established negative effects, environmental tobacco smoke (ETS) exposure remains highly prevalent worldwide. ETS exposure is associated with a wide range of physical and mental health-related problems among youth, including an increased likelihood to develop nicotine dependence. Up till now, neurocognitive effects of ETS exposure are largely unknown, while such effects could explain the role of ETS exposure in the development of nicotine dependence. Therefore, this preregistered study investigated the role of current ETS exposure in brain functioning associated with smoking cue-reactivity and inhibitory control.

METHOD

Concurrent with functional magnetic resonance imaging, nonsmoking adolescents aged 14-18 years (N = 51) performed a smoking cue-reactivity task, assessing brain functioning to smoking cues, and a Go/NoGo task measuring inhibitory control. ETS exposure was measured using a self-report questionnaire and biochemically verified.

RESULTS

No significant associations were observed between current ETS exposure and brain functioning associated with smoking cue-reactivity and inhibitory control.

CONCLUSION

These findings suggest that low-to-moderate levels of current ETS exposure are not associated with increased salience of smoking cues or deficits in inhibitory control in nonsmoking adolescents. Longitudinal research is needed to further clarify the exact effect of lifetime ETS exposure on brain functioning, as well as research focusing on the effects of higher levels of ETS exposure.

Effects of environmental tobacco smoke exposure on brain functioning in never-smoking adolescents

INTRODUCTION

Brain functioning, as indexed by event-related potentials (ERPs) representing smoking cue reactivity, inhibitory control, and reward processing, has been found to be compromised in smokers. However, whether environmental tobacco smoke (ETS) exposure in never smokers results in similar brain changes is unknown. This question is particularly relevant during adolescence, given ongoing brain maturation and a high risk of smoking initiation. The present study tested the associations between ETS exposure and ERPs reflecting cue reactivity (P3, LPP), inhibitory control (N2, P3), and reward processing (anticipation P3 (P3), feedback-related negativity (FRN)) among never-smoking adolescents.

METHODS

Eighty-four never-smoking adolescents (nonexposed = 32, exposed = 52) performed a smoking cue reactivity, a Go/NoGo, and a monetary incentive delay (MID) task while ERPs were measured.

RESULTS

Exposed and nonexposed groups did not differ in ERPs reflecting smoking cue reactivity, inhibitory control, and reward processing. A negative correlation between ETS exposure and the anticipatory P3 suggests reduced anticipatory reward sensitivity for nondrug rewards with increased levels of ETS exposure. However, since this effect was not consistent across analyses, no strong conclusions can be formulated. In the current study, few participants reported high levels of ETS exposure; therefore, further study is necessary.

CONCLUSIONS

Nevertheless, from this study, it can be concluded that low-to-moderate exposure to ETS during adolescence does not result in functional brain changes related to smoking cue reactivity, inhibitory control, and reward processing.

Examining the Role of Childhood Adversity on Excess Alcohol Intake and Tobacco Exposure among US College Students

BACKGROUND

Adverse childhood experiences (ACEs) are often associated with substance use behaviors such as drinking excess alcohol and tobacco use. Resilience may protect individuals from engaging in these maladaptive behaviors following ACEs. Objectives: We examined the associations between ACEs and excessive alcohol consumption, and ACEs and tobacco intake and exposure among diverse college students, and whether resilience buffered this relationship. Methods: We conducted a cross-sectional online survey in October 2018 with students at a large Southern university to assess ACEs, levels of resilience, and students' health behaviors. We used the Adverse Childhood Experiences - International Questionnaire (ACE-IQ) and the Brief Resilience Scale. Logistic regression modeled the relationship between ACEs and students' substance use behaviors. We adjusted for demographics, other health behaviors, and emotional health and we tested resilience as a possible buffer. Results: Participants (n = 568) were in their early twenties, almost three-fourths were female. We had a racially/ethnically diverse sample. Over two-thirds had experienced 1-4 ACEs. ACE exposure was not associated with excess alcohol consumption but exhibited a consistent dose-response relationship in unadjusted and adjusted models. Moderate ACEs increased the odds of tobacco exposure by 227% (OR: 3.27, 95% CI: 1.17-9.11) in adjusted models. Resilience was unrelated to either behavior. Black respondents had significantly reduced odds for both substance use outcomes. Tobacco exposure and excess alcohol intake were comorbid behaviors. Conclusion: Childhood adversity was a significant predictor for tobacco exposure among diverse US college students. Resilience did not buffer this relationship. Age, gender, and race/ethnicity were differentially associated with substance use.

Smoking Status Among Patients With Newly Diagnosed Lung Cancer in Taiwan

Background

Continued smoking after receiving a diagnosis of cancer seriously affects disease prognosis and survival. The prevalence and risk factors of continued smoking among patients with newly diagnosed lung cancer are unknown in Taiwan.

Purpose

The aims of this study were to assess the smoking status of patients with newly diagnosed lung cancer and to identify the characteristics that are associated with different smoking statuses.

Methods

Baseline data of a longitudinal study on smoking behaviors after lung cancer diagnosis were analyzed in this study. Patients were consecutively recruited from three medical centers in northern Taiwan. A structured questionnaire and medical chart reviews were used to collect data. Multinomial logistic regression analysis was used to examine the factors associated with continuing to smoke after being diagnosed with lung cancer.

Results

Among the 406 patients with newly diagnosed lung cancer who were recruited, 47.0% were never-smokers and 53.0% were ever-smokers. Among the second group, 38% were former smokers, 18% were recent quitters, and 44% were current smokers. Compared with former smokers, current smokers were more likely to be younger (OR = 1.05), to not exercise regularly (OR = 2.74), to currently live with smokers (OR = 2.48), and to have lower self-efficacy for refusing to smoke (OR = 0.95). Compared with recent quitters, current smokers were more likely to have lower self-efficacy for refusing to smoke.

Conclusions/Implications for Practice

A significant proportion of ever-smoker lung cancer patients in Taiwan will continue to smoke after receiving their diagnosis. Variables known to modify the risk factors associated with continued smoking such as regular exercise and better refusal self-efficacy should be considered and incorporated into future smoking cessation programs for patients with lung cancer.

Secondhand Smoke Exposure and Depressive Symptoms in Children: A Longitudinal Study

INTRODUCTION

We investigated whether secondhand smoke (SHS) exposure is associated with depressive symptoms in a population-based sample of children.

METHODS

Never-smoking students from 29 French-language elementary schools in Greater Montréal, Canada, were followed from 5th to 11th grade (2005-2011) in five waves: 1 (5th grade), 2 (spring 6th grade), 3 (7th grade), 4 (9th grade), and 5 (11th grade). Associations between depressive symptoms and SHS exposure at home and in cars were examined in cross-sectional and longitudinal gamma generalized regression models adjusted for sex, maternal education, and neighborhood socioeconomic status.

RESULTS

The sample comprised 1553 baseline never-smokers (mean [SD] age = 10.7 [0.5] years; 44% male; 89% French-speaking). SHS exposure at home and in cars was associated with higher depressive symptom scores in cross-sectional analyses pooled across grades and adjusted for demographics (B [95% confidence interval (CI)] = 0.041 [0.017 to 0.068] for home exposure; 0.057 [0.030 to 0.084] for car exposure). In longitudinal analyses from fifth to sixth grade, B (95% CI), adjusted for demographics and baseline depressive symptoms, was 0.042 (0.003 to 0.080) for home exposure and 0.061 (0.019 to 0.103) for car exposure. From sixth to seventh grade, B (95% CI) was 0.057 (0.003 to 0.110) for home exposure and 0.074 (0.015 to 0.133) for car exposure. SHS exposure at any age did not predict depressive symptoms 2 years later.

CONCLUSIONS

SHS exposure is associated with depressive symptoms in young persons, both concurrently and 1 year later. This finding adds to the evidence base supporting that children should be protected from SHS exposure.

IMPLICATIONS

SHS exposure has deleterious effects on physical health and results of this study raise concerns that such exposure might also affect the mental health of young persons. Clearly, protecting children from SHS in all locations is a critical public health priority. Although research is needed to determine if the association between SHS exposure and depressive symptoms is causal, continued implementation of smoking bans and educational efforts to discourage smoking in vehicles when children are present are warranted.

Addressing Ethnic Disparities in Adolescent Smoking: Is Reducing Exposure to Smoking in the Home a Key?

INTRODUCTION

Smoking among New Zealand (NZ) adolescents has declined since 2000, but ethnic disparities remain pronounced. To inform prevention efforts, we investigated exposure to and relative importance of known predictors of adolescent smoking and how these have changed over time, for Māori (NZ's indigenous population) and adolescents overall.

METHODS

We used repeat cross-sectional data, 2003-2015, from a national survey of 14- to 15-year olds (N = 20 443-31 696 per year). For the overall sample and for Māori and non-Māori, we calculated adjusted odds ratios (aORs) to assess the association between regular smoking and risk factors each year: one or more parents smoke, best friend smokes, older sibling(s) smoke, and past week exposure to smoking in the home. We calculated population attributable risk (PAR) for risk factors in 2003 and 2015.

RESULTS

Between 2003 and 2015, aORs for exposure to smoking in the home increased from 1.7 (95% CI 1.6% to 1.8%) to 2.6 (2.1% to 3.1%) overall and from 1.8 (1.6% to 2.1%) to 3.4 (2.5% to 4.5%) for Māori; aORs for "best friend smokes" also increased, while aORs for sibling smoking and parental smoking did not change meaningfully. PAR for exposure to smoking in the home increased from 17% to 31% overall and from 28% to 57% for Māori, while PARs for other risk factors decreased.

CONCLUSIONS

Exposure to smoking in the home has become more strongly associated with adolescent smoking over time and is an increasingly important risk factor at the population level (independent of parental smoking), particularly for Māori.

IMPLICATIONS

Our findings have implications for reducing smoking uptake and ethnic disparities in NZ, and potentially elsewhere, given the similarity in risk factors and trends for adolescent smoking internationally. Our findings suggest that reducing second-hand smoke exposure in homes will likely reduce uptake of smoking. Because Māori children are both more exposed and appear to be more strongly influenced by exposure to smoking in the home, interventions to reduce indoor smoking could have differentially positive effects for Māori. Greater research and policy attention to reducing smoking in homes is warranted.

Bidirectional Associations among Nicotine and Tobacco Smoke, NeuroHIV, and Antiretroviral Therapy

People living with HIV (PLWH) in the antiretroviral therapy (ART) era may lose more life-years to tobacco use than to HIV. Yet, smoking rates are more than twice as high among PLWH than the general population, contributing not just to mortality but to other adverse health outcomes, including neurocognitive deficits (neuroHIV). There is growing evidence that synergy with chronic inflammation and immune dysregulation that persists despite ART may be one mechanism by which tobacco smoking contributes to neuroHIV. This review will summarize the differential effects of nicotine vs tobacco smoking on inflammation in addition to the effects of tobacco smoke components on HIV disease progression. We will also discuss biomarkers of inflammation via neuroimaging as well as biomarkers of nicotine dependence (e.g., nicotine metabolite ratio). Tobacco smoking and nicotine may impact ART drug metabolism and conversely, certain ARTs may impact nicotine metabolism. Thus, we will review these bidirectional relationships and how they may contribute to neuroHIV and other adverse outcomes. We will also discuss the effects of tobacco use on the interaction between peripheral organs (lungs, heart, kidney) and subsequent CNS function in the context of HIV. Lastly, given the dramatic rise in the use of electronic nicotine delivery systems, we will discuss the implications of vaping on these processes. Despite the growing recognition of the importance of addressing tobacco use among PLWH, more research is necessary at both the preclinical and clinical level to disentangle the potentially synergistic effects of tobacco use, nicotine, HIV, cognition and immune dysregulation, as well as identify optimal approaches to reduce tobacco use. Graphical Abstract Proposed model of the relationships among HIV, ART, smoking, inflammation, and neurocognition. Solid lines represent relationships supported by evidence. Dashed lines represent relationships for which there is not enough evidence to make a conclusion. (a) HIV infection produces elevated levels of inflammation even among virally suppressed individuals. (b) HIV is associated with deficits in cognition function. (c) Smoking rates are higher among PLWH, compared to the general population. (d) The nicotine metabolite ratio (NMR) is associated with smoking behavior. (e) HIV and tobacco use are both associated with higher rates of psychiatric comorbidities, such as depression, and elevated levels of chronic stress. These factors may represent other mechanisms linking HIV and tobacco use. (f) The relationship between nicotine, tobacco smoking, and inflammation is complex, but it is well-established that smoking induces inflammation; the evidence for nicotine as anti-inflammatory is supported in some studies, but not others. (g) The relationship between tobacco use and neurocognition may differ for the effects of nicotine (acute nicotine use may have beneficial effects) vs. tobacco smoking (chronic use may impair cognition). (h) Elevated levels of inflammation may be associated with deficits in cognition. (i) PLWH may metabolize nicotine faster than those without HIV; the mechanism is not yet known and the finding needs validation in larger samples. We also hypothesize that if HIV-infection increases nicotine metabolism, then we should observe an attenuation effect once ART is initiated. (j) It is possible that the increase in NMR is due to ART effects on CYP2A6. (k) We hypothesize that faster nicotine metabolism may result in higher levels of inflammation since nicotine has anti-inflammatory properties.

Environmental tobacco smoke exposure among electronic cigarette users

INTRODUCTION

Exposure to environmental tobacco smoke (ETS) from combustible tobacco products causes various diseases and makes quitting smoking more difficult. However, little is known about exposure of e-cigarette users to ETS from combustible tobacco products. This study aimed to investigate e-cigarette users' exposure to ETS from tobacco smokers.

METHODS

The association between ETS exposure frequency and different types of smokers including e-cigarette users was examined using ordered logistic regression analysis and nationally representative survey data on 28,765 individuals who were interviewed in the Canadian Tobacco, Alcohol and Drugs Surveys conducted during 2013 and 2015. Survey respondents were classified into one of five smoker types: smokers of tobacco only, dual users of tobacco and e-cigarettes, users of e-cigarette only, former smokers and never smokers. The analyses were conducted using the entire sample and by age group.

RESULTS

Young to mid-age (15-54) dual users of both regular cigarettes and e-cigarettes have higher ETS exposure than even tobacco smokers. Young to mid-age single users of e-cigarettes are less exposed to ETS than tobacco smokers, but still have higher ETS than never smokers. At older age (55+), both dual and single e-cigarette users face similar risks of ETS exposure as tobacco smokers.

CONCLUSIONS

E-cigarette users are at high risk of ETS exposure. Policies that target the behaviour of e-cigarette users as well as the environments surrounding them to address their high ETS exposure risk would be beneficial.

Tobacco smoking and dopaminergic function in humans: a meta-analysis of molecular imaging studies

RATIONALE

About 1.1 billion people smoke tobacco globally and tobacco-related health care costs 1.8% of GDP in many countries. The majority of people are unable to quit smoking despite pharmacological intervention, highlighting the need to understand the pathophysiology associated with tobacco smoking to aid the development of new therapeutics. The reinforcing effects of tobacco smoking are thought to be mediated by the dopamine system. However, the nature of dopamine dysfunction seen in smokers is unclear.

OBJECTIVE

To determine the nature and robustness of the evidence for dopaminergic alterations in smokers.

METHODS

The entire MEDLINE, EMBASE, and PsycINFO databases were searched for studies from inception date to November 18, 2018. In vivo human molecular imaging studies of dopamine measures (dopamine synthesis or release capacity, transporter levels, receptor levels) in tobacco smokers were selected. Demographic, clinical, and imaging measures were extracted from each study and meta-analyses, and sensitivity analyses were conducted.

RESULTS

Fourteen studies met inclusion criteria comprising a total sample of 219 tobacco smokers and 297 controls. The meta-analysis showed a significant reduction in dopamine transporter availability in the smokers relative to controls with an effect size of - 0.72 ([95% CI, - 1.38 to - 0.05], p = 0.03). However, there was no difference in D2/3 receptor availability in smokers relative to controls (d = -0.16 ([95% CI, - 0.42 to 0.1], p = 0.23). There were insufficient studies for meta-analysis of other measures. However, findings from the published studies indicated blunted dopamine release and lower D1 receptor availability, while findings for dopamine synthesis capacity were inconsistent.

CONCLUSION

Our data indicate that striatal dopamine transporter availability is lower but D2/3 receptors are unaltered in smokers relative to controls. We discuss the putative mechanisms underlying this and their implications.

Effect of overnight smoking abstinence on a marker for microglial activation: a [11C]DAA1106 positron emission tomography study

RATIONALE

Microglia are the main immune cells in the central nervous system and participate in neuroinflammation. When activated, microglia express increased levels of the translocator protein 18 kDa (TSPO), thereby making TSPO availability a marker for neuroinflammation. Using positron emission tomography (PET) scanning, our group recently demonstrated that smokers in the satiated state had 16.8% less binding of the radiotracer [¹¹C]DAA1106 (a radioligand for TSPO) in the brain than nonsmokers.

OBJECTIVES

We sought to determine the effect of overnight smoking abstinence on [¹¹C]DAA1106 binding in the brain.

METHODS

Forty participants (22 smokers and 18 nonsmokers) completed the study (at one of two sites) and had usable data, which included images from a dynamic [¹¹C]DAA1106 PET scanning session (with smokers having been abstinent for 17.9 ± 2.3 h) and a blood sample for TSPO genotyping. Whole brain standardized uptake values (SUVs) were determined, and analysis of variance was performed, with group (overnight abstinent smoker vs. nonsmoker), site, and TSPO genotype as factors, thereby controlling for site and genotype.

RESULTS

Overnight abstinent smokers had lower whole brain SUVs (by 15.5 and 17.0% for the two study sites) than nonsmokers (ANCOVA, P = 0.004). The groups did not significantly differ in injected radiotracer dose or body weight, which were used to calculate SUV.

CONCLUSIONS

These results in overnight abstinent smokers are similar to those in satiated smokers, indicating that chronic cigarette smoking leads to global impairment of microglial activation which persists into early abstinence. Other explanations for study results, such as smoking leading to reduced numbers of microglia or smokers having more rapid metabolism of the radiotracer than nonsmokers, are also possible.

Why has adolescent smoking declined dramatically? Trend analysis using repeat cross-sectional data from New Zealand 2002-2015

OBJECTIVES

Adolescent smoking has declined in New Zealand and in many other countries since the late 1990s, yet the reasons for the decline are not well understood. We investigated the extent to which established risk factors for adolescent smoking (parental, sibling and peer smoking, and exposure to smoking in the home) explained the downward trend.

DESIGN

Trend analysis of repeat cross-sectional data from an annual nationally representative survey.

SETTING

New Zealand.

PARTICIPANTS

Secondary school students aged 14-15 (n=398 221).

OUTCOME MEASURE

Regular (at least monthly) smoking.

METHODS

For each risk factor (parental smoking, best friend smoking, older sibling smoking and past week exposure to smoking in the home) we plotted prevalence of exposure, 2002-2015. Next, using multivariable logistic regression, we modelled the trend in regular smoking (expressed as an OR for year) adjusting for age, sex, ethnicity and socioeconomic position. The risk factors were added to the model-individually and collectively-to test whether they attenuated the OR for year.

RESULTS

Exposure to all risk factors except 'past week exposure to smoking in the home' decreased between 2002 and 2015. We observed a strong downward trend in regular smoking among adolescents (OR=0.88 per year, 95% CI 0.88 to 0.88, p<0.001). 'Best friend smoking' was the only risk factor that significantly attenuated the trend. However, due to circularity, this factor provides an unsatisfactory explanation for population level smoking decline.

CONCLUSIONS

The established risk factors that we explored do not appear to have contributed to the remarkable decline in adolescent smoking in New Zealand between 2003 and 2015. Further research is needed to assess the possible contribution of factors outside our model, such as changes in the policy context, the social meaning of smoking and broader social and economic conditions.

Associations Between Secondhand Tobacco Smoke Exposure and Nicotine Dependence and Smoking Cessation Attempts Among Adult Tobacco Users With a Psychiatric Disorder

INTRODUCTION

Secondhand smoke exposure (SHSe) is predictive of greater nicotine dependence (ND) and poor smoking cessation (SC) outcomes. SHSe and its impact on ND and SC attempts in people with psychiatric disorders (PD) remain poorly understood. Hence, the objectives of this study were to (1) quantify SHSe, (2) examine the association of SHSe with ND, and (3) assess the association between SHSe and SC among tobacco users with PD.

METHOD

A cross-sectional survey of 118 tobacco users in an inpatient psychiatric facility was conducted. Data on demographics, tobacco use and SHSe history, motivation to quit smoking, ND, and SC attempts were obtained. Participants' environmental and psychosocial sources of and perceived SHSe were described. Multivariate linear regression analyses were used to examine the associations between SHSe and ND, while logistic regression analyses were used to assess the associations between SHSe and SC.

RESULTS

The primary sources of environmental SHSe were from the car (63.6%) and home (51.7%); primary sources of psychosocial SHSe were close friends (67.8%) and parents/grandparents (65.3%); and mean perceived SHSe was 6.2 ( SD = 3.5). Although perceived SHSe was significantly associated with ND (β = .39, p < .0001) in multivariate analyses, no SHSe variable was associated with SC. However, scores on items measuring motivation to quit smoking were associated with SC attempts.

DISCUSSION

Patients with PD reported high levels of SHSe, which was associated with higher ND. Routine screening for SHSe should be implemented as part of health assessments in this population to address ND treatment options. Moreover, targeted interventions and policies should be considered toward reducing SHSe in this vulnerable population.

A Stratified Meta-Analysis of the Association between Exposure to Environmental Tobacco Smoke during Childhood and Adulthood and Urothelial Bladder Cancer Risk

Background: Active smoking is a major risk factor for urothelial bladder cancer (UBC). However, the evidence that exposure to environmental tobacco smoke (ETS) either in childhood or adult life is also associated with UBC risk is ambiguous. With this meta-analysis, we aim to summarise how exposure to ETS is associated with UBC risk. Methods: In total, 11 studies (3 cohort studies, 8 case-control studies) were included in this meta-analysis and summary odds ratios (SORs) for UBC risk were calculated for never smokers who were exposed to ETS during childhood at home, during adulthood at home, or during adulthood in a work environment compared to never smokers who were never exposed to ETS. Sensitivity analyses were conducted to test the robustness of findings. Results: Never smokers exposed to ETS during childhood (SOR = 1.04, 95% confidence interval (CI) = 0.82-1.26), during adulthood at work (SOR = 0.98, 95% CI = 0.78-1.18) or at home (SOR = 0.99, 95% CI = 0.83-1.15) were at a similar risk of UBC compared to never smokers who were never exposed to ETS. Results for males and females were similar. Also, when pooling all estimates during both childhood and adulthood, no effect was observed (SOR = 1.00, 95% CI = 0.89-1.10). Conclusions: Although measurement of exposure to ETS was imprecise, there does not seem to be an association between UBC risk and exposure to ETS during childhood or adulthood. However, the current body of evidence mostly overlooks the duration and intensity of exposure to ETS.

Environmental Tobacco Exposure and Urinary Cotinine Levels in Smoking and Nonsmoking Adolescents

Objective

We aimed to evaluate the association between environmental tobacco smoke (ETS) exposure and urinary cotinine levels in current adolescent smokers and nonsmokers. The secondary objective was to explore the association between ETS exposure and nicotine dependence in adolescent smokers.

Methods

Using the results from a validation study for the 2012 Global Youth Tobacco Survey in Mexico, we quantified urinary cotinine levels in adolescent smokers and nonsmokers. We fitted a multivariate regression model to assess the association between household exposure to ETS and cotinine levels in adolescent smokers and nonsmokers. In addition, using the questionnaire's answers for morning cravings, we fitted a multivariate Poisson regression model to explore the association between household ETS exposure and nicotine dependence in adolescent smokers.

Results

For each day of household ETS exposure, cotinine levels increase by 5% in adolescent smokers compared to a 2% increase in nonsmokers, adjusting for the number of cigarettes smoked per week, age and sex (exp(β) 1.05; 95% confidence interval [CI] [1.00, 1.10]; p = .041). Morning cravings increase 11% for each day of household ETS exposure adjusting for the number of cigarettes smoked per week, age and sex (prevalence ratio [PR] 1.11; 95% CI [0.99, 1.25]; p = .064).

Conclusions

There is an association between ETS exposure and cotinine levels, and ETS may contribute to nicotine dependence in adolescent smokers. If confirmed, avoiding ETS exposure could prove helpful for addiction control and quitting in adolescents.

Implications

Evidence suggests that ETS increases cotinine levels in nonsmokers and adult smokers. However, no study has explored the association between ETS exposure and cotinine levels and addiction in adolescent smokers. This paper provides evidence of an association between ETS exposure and cotinine levels in adolescent smokers: each day of environmental tobacco smoke exposure at home increased cotinine levels by 5% among smokers. In addition, morning cravings in adolescent smokers increased 11% for every day of ETS exposure. ETS exposure is a significant source of nicotine for adolescent smokers and could play an important role in addiction.

Living with Smoker(s) and Smoking Cessation in Chinese Adult Smokers: Cross-Sectional and Prospective Evidence from Hong Kong Population Health Survey

Background: Results on the environmental influence on unassisted quitting are scarce. We investigated the associations of living with smoker(s) with quitting in Chinese adult smokers. Methods: We examined both cross-sectional and prospective data in the Hong Kong Population Health Survey recruited participants in 2003/04, and followed up to 2006. Unconditional logistic regression yielded adjusted odds ratios (AORs) of (i) planning to quit, (ii) ex-smoking (cross-sectional), and quitting (prospective) for living with smoker(s). 1679 ever smokers aged 18+ years at baseline, and 323 of them who were successfully followed-up were included in the cross-sectional, and prospective analysis. Results: At baseline, living with smoker(s) was significantly associated with lower odds of planning to quit in current smokers (AOR 0.41, 95% CI 0.25–0.68), and lower odds of ex-smoking (AOR 0.45, 95% CI 0.34–0.58), particularly if the smoker(s) smoked inside home (AOR 0.35, 95% CI 0.26–0.47). Prospectively, living with smoker(s) non-significantly predicted lower odds of new quitting (AOR 0.48, 95% CI 0.13–1.78). Conclusions: Our study has provided the first evidence in a Chinese general population that living with smoker(s) is an important barrier against smoking cessation. To boost quit rate in nonusers of smoking cessation services, smoking at home should be banned, especially for populations living in crowed urban environments that are typical of economically developed cities in China.

Airborne Nicotine, Secondhand Smoke, and Precursors to Adolescent Smoking

BACKGROUND AND OBJECTIVES

Secondhand smoke (SHS) directly increases exposure to airborne nicotine, tobacco's main psychoactive substance. When exposed to SHS, nonsmokers inhale 60% to 80% of airborne nicotine, absorb concentrations similar to those absorbed by smokers, and display high levels of nicotine biomarkers. Social modeling, or observing other smokers, is a well-established predictor of smoking during adolescence. Observing smokers also leads to increased pharmacological exposure to airborne nicotine via SHS. The objective of this study is to investigate whether greater exposure to airborne nicotine via SHS increases the risk for smoking initiation precursors among never-smoking adolescents.

METHODS

Secondary students (N = 406; never-smokers: n = 338, 53% girls, mean age = 12.9, SD = 0.4) participated in the AdoQuest II longitudinal cohort. They answered questionnaires about social exposure to smoking (parents, siblings, peers) and known smoking precursors (eg, expected benefits and/or costs, SHS aversion, smoking susceptibility, and nicotine dependence symptoms). Saliva and hair samples were collected to derive biomarkers of cotinine and nicotine. Adolescents wore a passive monitor for 1 week to measure airborne nicotine.

RESULTS

Higher airborne nicotine was significantly associated with greater expected benefits (R² = 0.024) and lower expected costs (R² = 0.014). Higher social exposure was significantly associated with more temptation to try smoking (R² = 0.025), lower aversion to SHS (R² = 0.038), and greater smoking susceptibility (R² = 0.071). Greater social exposure was significantly associated with more nicotine dependence symptoms; this relation worsened with higher nicotine exposure (cotinine R² = 0.096; airborne nicotine R² = 0.088).

CONCLUSIONS

Airborne nicotine exposure via SHS is a plausible risk factor for smoking initiation during adolescence. Public health implications include limiting airborne nicotine through smoking bans in homes and cars, in addition to stringent restrictions for e-cigarettes.

Mouse Models of COPD

Elastase and chronic cigarette smoke exposure animal models are commonly used to study lung morphologic and functional changes associated with emphysema-like airspace enlargement in various animal species. This chapter describes the rationale for using these two models to study mechanisms of COPD pathogenesis and provides protocols for their implementation. E-cigarettes are an emerging health concern and may also contribute to lung disease. Accordingly, approaches to study e-cigarette vapors are provided. This chapter also includes methods and tools necessary to assess lung morphologic and functional changes in animals with emphysema-like airspace enlargement.

Effect of Cigarette Smoking on a Marker for Neuroinflammation: A [11C]DAA1106 Positron Emission Tomography Study

In the brain, microglia continuously scan the surrounding extracellular space in order to respond to damage or infection by becoming activated and participating in neuroinflammation. When activated, microglia increase the expression of translocator protein (TSPO) 18 kDa, thereby making the TSPO expression a marker for neuroinflammation. We used the radiotracer [¹¹C]DAA1106 (a ligand for TSPO) and positron emission tomography (PET) to determine the effect of smoking on availability of this marker for neuroinflammation. Forty-five participants (30 smokers and 15 non-smokers) completed the study and had usable data. Participants underwent a dynamic PET scanning session with bolus injection of [¹¹C]DAA1106 (with smokers in the satiated state) and blood draws during PET scanning to determine TSPO affinity genotype and plasma nicotine levels. Whole-brain standardized uptake values (SUVs) were determined, and analysis of variance was performed, with group (smoker vs non-smoker) and genotype as factors, thereby controlling for genotype. Smokers and non-smokers differed in whole-brain SUVs (P=0.006) owing to smokers having 16.8% lower values than non-smokers. The groups did not differ in injected radiotracer dose or body weight, which were used to calculate SUV. An inverse association was found between whole-brain SUV and reported cigarettes per day (P<0.05), but no significant relationship was found for plasma nicotine. Thus, smokers have less [¹¹C]DAA1106 binding globally than non-smokers, indicating less microglial activation. Study findings are consistent with much prior research demonstrating that smokers have impaired inflammatory functioning compared with non-smokers and that constituents of tobacco smoke other than nicotine affect inflammatory processes.

Cholinergic Receptor Binding in Alzheimer Disease and Healthy Aging: Assessment In Vivo with Positron Emission Tomography Imaging

OBJECTIVE

To compare regional nicotinic cholinergic receptor binding in older adults with Alzheimer disease (AD) and healthy older adults in vivo and to assess relationships between receptor binding and clinical symptoms.

METHODS

Using cross-sectional positron emission tomography (PET) neuroimaging and structured clinical assessment, outpatients with mild to moderate AD (N = 24) and healthy older adults without cognitive complaints (C group; N = 22) were studied. PET imaging of α4β2* nicotinic cholinergic receptor binding using 2-[¹⁸F]fluoro-3-(2(S)azetidinylmethoxy)pyridine (2FA) and clinical measures of global cognition, attention/processing speed, verbal memory, visuospatial memory, and neuropsychiatric symptoms were used.

RESULTS

2FA binding was lower in the AD group compared with the C group in the medial thalamus, medial temporal cortex, anterior cingulate, insula/opercula, inferior caudate, and brainstem (p < 0.05, corrected cluster), but binding was not associated with cognition. The C group had significant inverse correlations between 2FA binding in the thalamus (left: r_s = -0.55, p = 0.008; right: r_s = -0.50, p = 0.02; N = 22) and hippocampus (left: r_s = -0.65, p = 0.001; right: r_s = -0.55, p = 0.009; N = 22) and the Trails A score. The AD group had inverse correlation between 2FA binding in anterior cingulate (left: r_s = -0.50, p = 0.01; right: r_s = -0.50, p = 0.01; N = 24) and Neurobehavioral Rating Scale agitation/disinhibition factor score.

CONCLUSION

Cholinergic receptor binding is reduced in specific brain regions in mild to moderate AD and is related to neuropsychiatric symptoms. Among healthy older adults, lower receptor binding may be associated with slower processing speed. Cholinergic receptor binding in vivo may reveal links to other key brain changes associated with aging and AD and may provide a potential molecular treatment target.

Nicotinic acetylcholine receptor availability in cigarette smokers: effect of heavy caffeine or marijuana use

RATIONALE

Upregulation of α4β2* nicotinic acetylcholine receptors (nAChRs) is one of the most well-established effects of chronic cigarette smoking on the brain. Prior research by our group gave a preliminary indication that cigarette smokers with concomitant use of caffeine or marijuana have altered nAChR availability.

OBJECTIVE

We sought to determine if smokers with heavy caffeine or marijuana use have different levels of α4β2* nAChRs than smokers without these drug usages.

METHODS

One hundred and one positron emission tomography (PET) scans, using the radiotracer 2-FA (a ligand for β2*-containing nAChRs), were obtained from four groups of males: non-smokers without heavy caffeine or marijuana use, smokers without heavy caffeine or marijuana use, smokers with heavy caffeine use (mean four coffee cups per day), and smokers with heavy marijuana use (mean 22 days of use per month). Total distribution volume (Vt/fp) was determined for the brainstem, prefrontal cortex, and thalamus, as a measure of nAChR availability.

RESULTS

A significant between-group effect was found, resulting from the heavy caffeine and marijuana groups having the highest Vt/fp values (especially for the brainstem and prefrontal cortex), followed by smokers without such use, followed by non-smokers. Direct between-group comparisons revealed significant differences for Vt/fp values between the smoker groups with and without heavy caffeine or marijuana use.

CONCLUSIONS

Smokers with heavy caffeine or marijuana use have higher α4β2* nAChR availability than smokers without these drug usages. These findings are likely due to increased nicotine exposure but could also be due to an interaction on a cellular/molecular level.

Nicotinic alteration of functional thalamocortical topography

The thalamocortical pathways form highly topographic connections from the primary sensory thalamic nuclei to the primary cortical areas. The synaptic properties of these thalamocortical connections are modifiable by activation from various neuromodulators, such as acetylcholine. Cholinergic activation can alter functional properties in both the developing and the mature nervous system. Moreover, environmental factors, such as nicotine, can activate these receptors, although the circuit-level alterations resulting from such nicotinic activation of sensory neural circuits remain largely unexplored. Therefore, we examined alterations to the functional topography of thalamocortical circuits in the developing sensory pathways of the mouse. Photostimulation by uncaging of glutamate was used to map these functional thalamocortical alterations in response to nicotinic receptor activation. As a result, we found that activation of forebrain nicotinic acetylcholine receptors results in an expansion and enhancement of functional thalamocortical topographies as assessed in brain slice preparations using laser-scanning photostimulation by uncaging of glutamate. These physiological changes were correlated with the neuroanatomical expression of nicotinic acetylcholine receptor subtypes (α7 and β2). These circuit-level alterations may provide a neural substrate underlying the plastic development and reshaping of thalamocortical circuitry in response to nicotinic receptor activation.

PET imaging for addiction medicine: From neural mechanisms to clinical considerations

Positron emission tomography (PET) has been shown to be an effective imaging technique to study neurometabolic and neurochemical processes involved in addiction. That is, PET has been used to research neurobiological differences in substance abusers versus healthy controls and the pharmacokinetics and pharmacodynamics of abused drugs. Over the past years, the research scope has shifted to investigating neurobiological effects of abstinence and treatment, and their predictive power for relapse and other clinical outcomes. This chapter provides an overview of PET methodology, recent human PET studies on drug addiction and their implications for clinical treatment.

Parental smoke exposure and the development of nicotine craving in adolescent novice smokers: the roles of DRD2, DRD4, and OPRM1 genotypes

BACKGROUND

Among adolescent novice smokers, craving is often the first, and is the most reported, symptom of nicotine dependence. Until now, little has been known about the development of craving symptoms in novice smokers. The aim of this study was to identify specific genetic (i.e., DRD2 Taq1A, DRD4 48 bp VNTR, and OPRM1 A118G polymorphisms) and environmental mechanisms that underlie the emergence of both cue-induced and cognitive craving among adolescent novice smokers.

METHOD

A five-wave longitudinal, genetically-informed survey study was conducted with intervals of four months. The sample included 376 early adolescent smokers (12-13 years of age at baseline). Self-report questionnaires were completed regarding smoking behavior, observed parental smoking behavior, and both cue-induced and cognitive craving.

RESULTS

Data were analyzed with a latent growth curve approach. For both cue-induced and cognitive craving, significant interaction effects were found for DRD2 Taq1A with parental smoke exposure. A1-allele carriers did not seem to be influenced by the environment with regard to craving development. Adolescents who are homozygous for the A2-allele and who are more exposed to parental smoking experience the highest levels of both types of craving over time. No significant interaction effects were found between parental smoke exposure and DRD4 48 bp VNTR or OPRM1 A118G.

CONCLUSIONS

Previous studies identified DRD2 Taq1A A1-allele carriers as vulnerable to developing nicotine dependence. However, this study showed that parental smoking increased the chances of developing dependence more rapidly for early adolescents who are considered to be less sensitive to the rewarding effects of nicotine according to their DRD2 Taq1A genotype. It is thus especially important that these young people not be exposed to smoking in their social environment.

Bacoside A: Role in Cigarette Smoking Induced Changes in Brain

Cigarette smoking (CS) is a major health hazard that exerts diverse physiologic and biochemical effects mediated by the components present and generated during smoking. Recent experimental studies have shown predisposition to several biological consequences from both active and passive cigarette smoke exposure. In particular, passive smoking is linked to a number of adverse health effects which are equally harmful as active smoking. A pragmatic approach should be considered for designing a pharmacological intervention to combat the adverse effects of passive smoking. This review describes the results from a controlled experimental condition, testing the effect of bacoside A (BA) on the causal role of passive/secondhand smoke exposure that caused pathological and neurological changes in rat brain. Chronic exposure to cigarette smoke induced significant changes in rat brain histologically and at the neurotransmitter level, lipid peroxidation states, mitochondrial functions, membrane alterations, and apoptotic damage in rat brain. Bacoside A is a neuroactive agent isolated from Bacopa monnieri. As a neuroactive agent, BA was effective in combating these changes. Future research should examine the effects of BA at molecular level and assess its functional effects on neurobiological and behavioral processes associated with passive smoke.

Decreased Nicotinic Receptor Availability in Smokers with Slow Rates of Nicotine Metabolism

The nicotine metabolite ratio (NMR), a stable measure of hepatic nicotine metabolism via the CYP2A6 pathway and total nicotine clearance, is a predictive biomarker of response to nicotine replacement therapy, with increased quit rates in slower metabolizers. Nicotine binds directly to nicotinic acetylcholine receptors (nAChRs) to exert its psychoactive effects. This study examined the relationship between NMR and nAChR (α4β2* subtype) availability using PET imaging of the radiotracer 2-(18)F-fluoro-3-(2(S)-azetidinylmethoxy)pyridine (2-(18)F-FA-85380, or 2-(18)F-FA).

METHODS

Twenty-four smokers-12 slow metabolizers (NMR < 0.26) and 12 normal metabolizers (NMR ≥ 0.26)-underwent 2-(18)F-FA-PET brain imaging after overnight nicotine abstinence (18 h before scanning), using a validated bolus-plus-infusion protocol. Availability of nAChRs was compared between NMR groups in a priori volumes of interest, with total distribution volume (VT/fP) being the measure of nAChR availability. Cravings to smoke were assessed before and after the scans.

RESULTS

Thalamic nAChR α4β2* availability was significantly reduced in slow nicotine metabolizers (P = 0.04). Slow metabolizers exhibited greater reductions in cravings after scanning than normal metabolizers; however, craving was unrelated to nAChR availability.

CONCLUSION

The rate of nicotine metabolism is associated with thalamic nAChR availability. Additional studies could examine whether altered nAChR availability underlies the differences in treatment response between slow and normal metabolizers of nicotine.

A systematic review of secondhand tobacco smoke exposure and smoking behaviors: Smoking status, susceptibility, initiation, dependence, and cessation

OBJECTIVES

To examine the association between secondhand tobacco smoke exposure (SHSe) and smoking behaviors (smoking status, susceptibility, initiation, dependence, and cessation).

METHODS

Terms and keywords relevant to smoking behaviors and secondhand tobacco smoke exposure were used in a search of the PubMed database. Searches were limited to English language peer-reviewed studies up till December 2013. Included papers: a) had clearly defined measures of SHSe and b) had clearly defined measures of outcome variables of interest. A total of 119 studies were initially retrieved and reviewed. After further review of references from the retrieved studies, 35 studies were finally selected that met all eligibility criteria.

RESULTS

The reviewed studies consisted of thirty-five (89.7%) studies with differing measures of SHSe (including questionnaire and biological measures) and varying definitions of main outcome variables of interest between studies. The majority of the studies (77%) were cross-sectional in nature. The majority of studies found that SHSe was associated with greater likelihood of being a smoker, increased susceptibility and initiation of smoking, greater nicotine dependence among nonsmokers, and poorer smoking cessation.

CONCLUSIONS

The review found positive associations between SHSe and smoking status, susceptibility, initiation and nicotine dependence and a negative association with smoking cessation. In light of design limitations, future prospective and clinical studies are needed to better understand the mechanisms whereby SHSe influences smoking behaviors.

Prospective Associations Between Early Long-Term Household Tobacco Smoke Exposure and Subsequent Indicators of Metabolic Risk at Age 10

INTRODUCTION

Although there are established risks associated with gestational tobacco smoke exposure, few studies have addressed the metabolic hazards of domestic exposure in early childhood. This study prospectively examines the long-term relationship between early childhood exposure to household smoke and two adiposity-related measures at age 10.

METHODS

Participants from the Quebec Longitudinal Study of Child Development birth cohort were categorized into one of three groups of early childhood household exposure to tobacco smoke over four time points (from ages 1 to 7 years): never-exposed; transient exposure; and continuous exposure. Follow-up measures of body mass index and waist circumference were independently assessed at age 10.

RESULTS

Compared to being never exposed, transient and continuous household smoke exposure predicted increases of 0.93 cm (95% confidence interval [CI] between 0.05 and 1.82 cm; P = .03) and 1.56 cm (95% CI between 0.07 and 3.05 cm; P = .04) in children's waist circumference, respectively. Children exposed to transient and continuous household smoke, compared to unexposed children, also showed 0.48 and 0.81 point increases in their body mass index, respectively, both Ps = .005. Once adjusted, for confounding variables, only transient household smoke remained associated with 43% greater odds of belonging to the overweight/obese category (95% CI between 1.12 and 1.81 cm; P < .01).

CONCLUSIONS

We found significant long-term prospective associations between home-based secondhand smoke exposure and unhealthy body fat distribution. Waist circumference in youth has become an important risk factor for obesity-related diseases in adulthood. Our findings emphasize the importance public health initiatives and parental sensitization aimed at domestic exposure reductions during the critical early childhood years.

Behavioral and Physiological Responses to Nicotine Patch Administration Among Nonsmokers Based on Acute and Chronic Secondhand Tobacco Smoke Exposure

INTRODUCTION

Despite the large amount that is known about the physical health effects of secondhand tobacco smoke (SHS) exposure, little is known about the behavioral health effects. Nicotine, the principle psychoactive substance in SHS, elicits subjective mood and physiological responses in nonsmokers. However, no studies have examined the subjective mood or physiological responses to nicotine in nonsmokers while accounting for prior chronic or acute SHS exposure.

METHODS

A 7-mg nicotine patch was administered to 17 adult nonsmokers for 2 hr. Main outcome measures obtained at ½ hr, 1 hr, and 2 hr were subjective behavioral drug effects (based on eleven 10-cm Visual Analog Scales [VASs]) and the physiological measures of heart rate, blood pressure, and serum nicotine levels. Analysis of outcome data was based on participants' chronic (using hair nicotine) or acute (using saliva cotinine) SHS exposure.

RESULTS

Greater chronic SHS exposure was negatively associated with pleasurable responses to nicotine administration ("drug feels good" score at 2-hr time point, Spearman's ρ = -.65, p < .004), whereas greater acute SHS exposure was associated with positive responses ("like feeling of drug" score at 2-hr time point, Spearman's ρ = .63, p < .01). There were no associations between chronic or acute exposure and physiological changes in response to nicotine administration.

DISCUSSION

The findings of this study may be useful in providing preliminary empirical data for future explorations of the mechanism whereby SHS exposure can influence behavioral outcomes in nonsmokers. Such studies can inform future interventions to reduce the physical and behavioral health risks associated with SHS exposure.

Inside-out neuropharmacology of nicotinic drugs

Upregulation of neuronal nicotinic acetylcholine receptors (AChRs) is a venerable result of chronic exposure to nicotine; but it is one of several consequences of pharmacological chaperoning by nicotine and by some other nicotinic ligands, especially agonists. Nicotinic ligands permeate through cell membranes, bind to immature AChR oligomers, elicit incompletely understood conformational reorganizations, increase the interaction between adjacent AChR subunits, and enhance the maturation process toward stable AChR pentamers. These changes and stabilizations in turn lead to increases in both anterograde and retrograde traffic within the early secretory pathway. In addition to the eventual upregulation of AChRs at the plasma membrane, other effects of pharmacological chaperoning include modifications to endoplasmic reticulum stress and to the unfolded protein response. Because these processes depend on pharmacological chaperoning within intracellular organelles, we group them as "inside-out pharmacology". This term contrasts with the better-known, acute, "outside-in" effects of activating and desensitizing plasma membrane AChRs. We review current knowledge concerning the mechanisms and consequences of inside-out pharmacology. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.

Imaging Tobacco Smoking with PET and SPECT

Receptor imaging, including positron emission computed tomography (PET) and single photon emission computed tomography (SPECT), provides a way to measure chemicals of interest, such as receptors, and neurotransmitter fluctuations, in the living human brain. Imaging the neurochemical mechanisms involved in the maintenance and recovery from tobacco smoking has provided insights into critical smoking related brain adaptations. Nicotine, the primary addictive chemical in tobacco smoke, enters the brain, activates beta2-nicotinic acetylcholine receptors (β2*-nAChRs) and, like most drugs of abuse, elicits dopamine (DA) release in the ventral striatum. Both β2*-nAChRs and DA signaling are critical neurosubstrates underlying tobacco smoking behaviors and dependence and have been studied extensively with PET and SPECT brain imaging. We review the imaging literature on these topics and describe how brain imaging has helped inform the treatment of tobacco smoking.

Secondhand smoke exposure and serum cotinine levels among current smokers in the USA

BACKGROUND

Secondhand smoke (SHS) likely provides additional exposure to nicotine and toxins for smokers, but has been understudied. Our objective was to determine whether SHS exposure among smokers yields detectable differences in cotinine levels compared with unexposed smokers at the population level.

METHODS

Using the US National Health and Nutrition Examination Survey (NHANES) for the years 1999-2012, we compared serum cotinine levels of 4547 current adult cigarette smokers stratified by self-reported SHS exposure sources (home and/or work) and smoking intensity. A weighted multivariable linear regression model determined the association between SHS exposure and cotinine levels among smokers.

RESULTS

Smokers with SHS exposure at home (43.8%) had higher cotinine levels (β=0.483, p≤0.001) compared with those with no SHS exposure at home after controlling for the number of cigarettes smoked per day and number of days smoked in the previous 5 days, survey year, age, gender and education. Smokers with SHS exposure at work (20.0%) did not have significantly higher cotinine levels after adjustment. The adjusted geometric mean cotinine levels of light smokers (1-9 cigarettes per day) with no SHS exposure, exposure at work only, home only, and both home and work were 52.0, 62.7, 67.2, 74.4 ng/mL, respectively, compared with 219.4, 220.9, 255.2, 250.5 ng/mL among moderate/heavy smokers (≥10 cigarettes per day).

CONCLUSIONS

Smokers living in residences where others smoke inside the home had significantly higher cotinine levels than smokers reporting no SHS exposure, regardless of individual smoking intensity. Future research should target the role that SHS exposure may have in nicotine dependence, cessation outcomes and other health impacts among smokers.

Dual role of nicotine in addiction and cognition: a review of neuroimaging studies in humans

Substantial evidence demonstrates both nicotine's addiction liability and its cognition-enhancing effects. However, the neurobiological mechanisms underlying nicotine's impact on brain function and behavior remain incompletely understood. Elucidation of these mechanisms is of high clinical importance and may lead to improved therapeutics for smoking cessation as well as for a number of cognitive disorders such as schizophrenia. Neuroimaging techniques such as positron emission tomography (PET), single photon emission computed tomography (SPECT), and functional magnetic resonance imaging (fMRI), which make it possible to study the actions of nicotine in the human brain in vivo, play an increasingly important role in identifying these dual mechanisms of action. In this review, we summarize the current state of knowledge and discuss outstanding questions and future directions in human neuroimaging research on nicotine and tobacco. This research spans from receptor-level PET and SPECT studies demonstrating nicotine occupancy at nicotinic acetylcholine receptors (nAChRs) and upregulation of nAChRs induced by chronic smoking; through nicotine's interactions with the mesocorticolimbic dopamine system believed to mediate nicotine's reinforcing effects leading to dependence; to functional activity and connectivity fMRI studies documenting nicotine's complex behavioral and cognitive effects manifest by its actions on large-scale brain networks engaged both during task performance and at rest. This article is part of the Special Issue Section entitled 'Neuroimaging in Neuropharmacology'.

Neuroimaging in Alcohol and Drug Dependence

Neuroimaging, including PET, MRI, and MRS, is a powerful approach to the study of brain function. This article reviews neuroimaging findings related to alcohol and other drugs of abuse that have been published since 2011. Uses of neuroimaging are to characterize patients to determine who will fare better in treatment and to investigate the reasons underlying the effect on outcomes. Neuroimaging is also used to characterize the acute and chronic effects of substances on the brain and how those effects are related to dependence, relapse, and other drug effects. The data can be used to provide encouraging information for patients, as several studies have shown that long-term abstinence is associated with at least partial normalization of neurological abnormalities.

Comprehensive smoke-free policies: a tool for improving preconception health?

Lower income women are at higher risk for preconception and prenatal smoking, are less likely to spontaneously quit smoking during pregnancy, and have higher prenatal relapse rates than women in higher income groups. Policies prohibiting tobacco smoking in public places are intended to reduce exposure to secondhand smoke; additionally, since these policies promote a smoke-free norm, there have been associations between smoke-free policies and reduced smoking prevalence. Given the public health burden of smoking, particularly among women who become pregnant, our objective was to assess the impact of smoke-free policies on the odds of preconception smoking among low-income women. We estimated the odds of preconception smoking among low-income women in Ohio between 2002 and 2009 using data from repeated cross-sectional samples of women participating in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). A logistic spline regression was applied fitting a knot at the point of enforcement of the Ohio Smoke-free Workplace Act to evaluate whether this policy was associated with changes in the odds of smoking. After adjusting for individual- and environmental-level factors, the Ohio Smoke-free Workplace Act was associated with a small, but statistically significant reduction in the odds of preconception smoking in WIC participants. Comprehensive smoke-free policies prohibiting smoking in public places and workplaces may also be associated with reductions in smoking among low-income women. This type of policy or environmental change strategy may promote a tobacco-free norm and improve preconception health among a population at risk for smoking.

A positive relationship between harm avoidance and brain nicotinic acetylcholine receptor availability

Prior research indicates that disturbance of cholinergic neurotransmission reduces anxiety, leading to the hypothesis that people with heightened cholinergic function have a greater tendency toward anxiety-like and/or harm-avoidant behavior. We sought to determine if people with elevated levels of harm avoidance (HA), a dimension of temperament from the Temperament and Character Inventory (TCI), have high α4β2* nicotinic acetylcholine receptor (nAChR) availability. Healthy adults (n=105; 47 non-smokers and 58 smokers) underwent bolus-plus-continuous infusion positron emission tomography (PET) scanning using the radiotracer 2-[18F]fluoro-3-(2(S)azetidinylmethoxy) pyridine (abbreviated as 2-FA). During the uptake period of 2-FA, participants completed the TCI. The central study analysis revealed a significant association between total HA and mean nAChR availability, with higher total HA scores being linked with greater nAChR availability. In examining HA subscales, both 'Fear of Uncertainty' and 'Fatigability' were significant, based on higher levels of these characteristics being associated with greater nAChR availabilities. This study adds to a growing body of knowledge concerning the biological basis of personality and may prove useful in understanding the pathophysiology of psychiatric disorders (such as anxiety disorders) that have similar characteristics to HA. Study findings may indicate that heightened cholinergic neurotransmission is associated with increased anxiety-like traits.

Exposure to environmental tobacco smoke and risk of antenatal depression: application of latent variable modeling

This study sought to determine the impact of passive smoking on the risk for depressive symptoms during pregnancy. In this prospective study, 236 pregnant women were recruited at less than 20 weeks of gestation from a university-affiliated obstetric clinic from November 2009 through July 2011. Tobacco use/exposure was measured using questionnaire and confirmed by salivary cotinine analysis. The Edinburgh Perinatal Depression Scale (EPDS) was employed to capture perinatal depressive symptomatology. Traditionally, a cutoff of 13 is utilized to indicate depressive symptoms in the perinatal population. However, this approach is vulnerable to measurement errors that are inherent in assessing depression using cutoff points. Therefore, in this analysis, we apply a flexible approach (latent variable modeling) that accounts for measurement errors thereby reducing bias in the estimates of association. Significant differences were observed in the mean EPDS scores across non-smokers (mean ± SD = 4.8 ± 4.8), passive smokers (5.3 ± 5.5) and active smokers (7.4 ± 6.1) [p value = 0.02]. For each itemized response of the EPDS, passive smokers demonstrated an increased risk for depressive symptoms with the greatest risk exhibited by items 8 and 9 of the questionnaire (feeling sad or miserable and feeling unhappy [and]crying, respectively). In addition, for each item of the EPDS, a dose-response pattern was revealed with non-smokers having the least risk of depressive symptoms during pregnancy and active smokers having the greatest risk. Women who are exposed to secondhand smoke are at elevated risk for depressive symptoms during pregnancy.

Treatment for tobacco dependence: effect on brain nicotinic acetylcholine receptor density

Cigarette smoking leads to upregulation of brain nicotinic acetylcholine receptors (nAChRs), including the common α4β2* nAChR subtype. Although a substantial percentage of smokers receive treatment for tobacco dependence with counseling and/or medication, the effect of a standard course of these treatments on nAChR upregulation has not yet been reported. In the present study, 48 otherwise healthy smokers underwent positron emission tomography (PET) scanning with the radiotracer 2-FA (for labeling α4β2* nAChRs) before and after treatment with either cognitive-behavioral therapy, bupropion HCl, or pill placebo. Specific binding volume of distribution (VS/fP), a measure proportional to α4β2* nAChR density, was determined for regions known to have nAChR upregulation with smoking (prefrontal cortex, brainstem, and cerebellum). In the overall study sample, significant decreases in VS/fP were found for the prefrontal cortex, brainstem, and cerebellum of -20 (±35), -25 (±36), and -25 (±31)%, respectively, which represented movement of VS/fP values toward values found in non-smokers (mean 58.2% normalization of receptor levels). Participants who quit smoking had significantly greater reductions in VS/fP across regions than non-quitters, and correlations were found between reductions in cigarettes per day and decreases in VS/fP for brainstem and cerebellum, but there was no between-group effect of treatment type. Thus, smoking reduction and cessation with commonly used treatments (and pill placebo) lead to decreased α4β2* nAChR densities across brain regions. Study findings could prove useful in the treatment of smokers by providing encouragement with the knowledge that decreased smoking leads to normalization of specific brain receptors.

Animal models of nicotine exposure: relevance to second-hand smoking, electronic cigarette use, and compulsive smoking

Much evidence indicates that individuals use tobacco primarily to experience the psychopharmacological properties of nicotine and that a large proportion of smokers eventually become dependent on nicotine. In humans, nicotine acutely produces positive reinforcing effects, including mild euphoria, whereas a nicotine abstinence syndrome with both somatic and affective components is observed after chronic nicotine exposure. Animal models of nicotine self-administration and chronic exposure to nicotine have been critical in unveiling the neurobiological substrates that mediate the acute reinforcing effects of nicotine and emergence of a withdrawal syndrome during abstinence. However, important aspects of the transition from nicotine abuse to nicotine dependence, such as the emergence of increased motivation and compulsive nicotine intake following repeated exposure to the drug, have only recently begun to be modeled in animals. Thus, the neurobiological mechanisms that are involved in these important aspects of nicotine addiction remain largely unknown. In this review, we describe the different animal models available to date and discuss recent advances in animal models of nicotine exposure and nicotine dependence. This review demonstrates that novel animal models of nicotine vapor exposure and escalation of nicotine intake provide a unique opportunity to investigate the neurobiological effects of second-hand nicotine exposure, electronic cigarette use, and the mechanisms that underlie the transition from nicotine use to compulsive nicotine intake.